Charged particle beam apparatus

ABSTRACT

A sample measuring method and a charged particle beam apparatus are provided which remove contaminants, that have adhered to a sample in a sample chamber of an electron microscope, to eliminate adverse effects on the subsequent manufacturing processes. To achieve this objective, after the sample measurement or inspection is made by using a charged particle beam, contaminants on the sample are removed before the next semiconductor manufacturing process. This allows the contaminants adhering to the sample in the sample chamber to be removed and therefore failures or defects that may occur in a semiconductor fabrication process following the measurement and inspection can be minimized.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Continuation application of application Ser. No.11/305,109, filed Dec. 19, 2005, which claims priority from JapanesePatent Application No. 2005-344855, filed Nov. 30, 2005, the contents ofwhich are incorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

The present invention relates to a sample measuring method and a chargedparticle beam apparatus and more specifically to a charged particle beamapparatus that does not contaminate the sample.

A process assessment is performed by measuring a pattern width as by aCD-SEM (Critical Dimension-Scanning Electron Microscope) after resistapplication, exposure and development. More specifically, to check by ascanning electron microscope represented by CD-SEM whether a patternformed on a sample such as semiconductor wafer is properly formed, asample is moved by a sample stage so that an electron beam can beradiated against a desired pattern.

In such an apparatus, if a contaminant is adhering to a surface of thesample, scanning an electron beam over a portion where the contaminantis present means that the electron beam scans the surface of thecontaminant, making it impossible to produce a true sample image orobtain correct measurements of sample dimensions. A technique to solvethis problem is disclosed in Patent Document 1.

JP-A-11-329328 proposes that, before introducing a sample into a samplechamber in an electron beam inspection apparatus, the sample is heatedby a heater installed in a preliminary exhaust chamber of the electronbeam inspection apparatus to remove the contaminant. It is alsodescribed in JP-A-5-135752 that, when the sample examination is notperformed, an organic gas produced from grease used in the sample stageis removed by heating it to 50-60° C.

It has been found in recent years that contaminants may adhere tosemiconductor wafers as they undergo measurement or inspection by ascanning electron microscope. If these contaminants adhere to asemiconductor wafer, air bubbles may be formed in a resist during asubsequent resist application process. Because of the air bubbles, theresist may be formed thin, which in turn will likely to result inanother problem that pits may be formed in a base material during a dryetch process.

Investigations by the authors of this invention have found thatcontaminants adhering to the sample are fluorocompounds used as alubricant in the electron microscope. The fluorocompounds can mostly beremoved if subjected to a cleaning process. However, to shorten the timetaken by the semiconductor manufacturing process as much as possible, itis desired that the sample be transferred directly to the resistapplication process following the measurement or inspection by thescanning electron microscope, without undergoing the cleaning process.

The technique disclosed in JP-A-11-329328 performs heating of the samplebefore introducing the sample into the sample chamber. This cantemporarily remove the contaminants. However, contaminants that adhereto the sample in the sample chamber remain on the sample, giving rise toa problem that the contaminants can cause failures in the subsequentmanufacturing process.

Further, as disclosed in JP-A-5-135752, it is conceivable to heat thesample chamber. Since materials that are weak to heat, such as O-ring,are used in some cases in the sample chamber, heating the sample chamberitself is not preferred. Vaporized grease may adhere to inner walls ofthe sample chamber, from which it may fly to the sample.

SUMMARY OF THE INVENTION

An object of this invention is to provide a sample measuring method anda charged particle beam apparatus which can remove contaminants adheringto a sample in the sample chamber of an electron microscope and suppresstheir adverse effects on the subsequent manufacturing process.

To achieve the above objective, an apparatus is provided which executesa sample contaminant removing process prior to the next semiconductormanufacturing process after the sample measurement or inspection by thecharged particle beam has been made. Other constructions and embodimentsof this invention will be described in detail in the section ofpreferred embodiment of the invention.

With this invention, because contaminants adhering to a sample in thesample chamber can be removed, failures that may occur in thesemiconductor fabrication process following the measurement andinspection can be minimized.

Other objects, features and advantages of the invention will becomeapparent from the following description of the embodiments of theinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing an outline configuration of ascanning electron microscope.

FIG. 2 shows a scanning electron microscope incorporating a sampleheating device.

FIG. 3 is a flow chart showing a sequence of processing from a step ofperforming a measurement/inspection using an electron beam to a step ofmounting a wafer on a wafer cassette.

FIG. 4 illustrates a configuration of an electron microscopeincorporating a device for measuring contaminants in the sample chamber.

FIG. 5 is a graph representing a case where low-molecular weightcompounds are not detected in the sample chamber.

FIG. 6 is a graph representing a case where low-molecular weightcompound are detected in the sample chamber.

FIG. 7 illustrates a configuration of an electron microscopeincorporating a heating/cooling mechanism capable of heating inner wallsof the sample chamber.

FIG. 8 illustrates a configuration of an electron microscopeincorporating a voltage control, electrode to control a voltage in aspace in which a sample is installed.

FIG. 9 illustrates a configuration of an electron microscopeincorporating a heating/cooling mechanism capable of directly heatingthe sample stage.

FIG. 10 is a plan view of a charged particle beam apparatus and aload-lock chamber.

FIG. 11 is a diagram of a sequence for holding a wafer in a standbystate, with an interior of the load-lock chamber maintained at theatmospheric pressure.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows an outline configuration of a scanning electron microscopeas one example of this invention. A controller 1 controls an opticalsystem control device 2, a stage control device 3, a sample deliverycontrol device 4, and a sample exchange chamber control device 5according to an acceleration voltage, sample (semiconductor device)information, measurement position information and wafer cassetteinformation entered by an operator from a user interface not shown.

Upon receiving a command from the controller 1, the sample deliverycontrol device 4 controls a transport robot 8 to move a desired wafer 7from a wafer cassette 6 to a desired position in the sample exchangechamber 9. In connection with the wafer 7 being carried into or out ofthe load-lock chamber 9, the sample exchange chamber control device 5controls the open-close operation of gate valves 10, 11. Further, thesample exchange chamber control device 5 controls a vacuum pump (notsown) to evacuate the interior of the sample exchange chamber 9 tocreate the same level of vacuum as that of the sample chamber 12 in thesample exchange chamber 9 when the gate valve 11 is open. The wafer 7introduced into the sample exchange chamber 9 is transported into thesample chamber 12 through the gate valve 11 and fixed on a stage 13.

The optical system control device 2, according to a command from thecontroller 1, controls a high voltage control device 14, a condenserlens control unit 15, an amplifier 16, a deflection signal control unit17, and an object lens control unit 18.

An electron beam 21 drawn out from an electron source 20 by a drawoutelectrode 19 is focused by a condenser lens 22 and an object lens 23 andradiated against the wafer 7 placed on the stage 13. The electron beam21 is scanned over the wafer 7 one- or two-dimensionally by a deflector24 that receives a signal from the deflection signal control unit 17.

Secondary charged particles 25, released from the wafer as a result ofradiation of the electron beam 21 onto the wafer 7, are transformed by asecondary electron conversion electrode 27 into secondary electrons 28,which are arrested by a secondary charged particle detector 29 and thenused via an amplifier 16 as a luminance signal for a screen of a display26.

A pattern configuration on the wafer can be reproduced on the display 26by synchronizing a deflection signal of the display 26 with a deflectionsignal of the deflector 24.

Embodiment 1

FIG. 2 represents an example of this invention in which a heating devicefor a sample (semiconductor wafer) is installed between the load-lockchamber 9 and the wafer cassette 6. In this example, a process will bedescribed in which the wafer 7, after completing the measurement andinspection by the electron beam, passes between two heaters 30 and thenthrough a cooling mechanism 31 before returning into the wafer cassette6. The heaters are provided with an exhaust unit not shown. In thisexample, the heaters use a resistive heating type hot plate 30. Coolplates (cooling mechanism) 31 employed are of a water-cooled type.

Possible examples of replacement of the heaters include a lamp heatingdevice and a member through which a hot medium flows.

The wafer 7, after completing the measurement, is placed on the hotplate 30 by the robot 8. The hot plate 30 is preheated to apredetermined temperature by a hot plate control device 33 and beginsheating when the wafer 7 is placed on it. The hot plate 30 and the coolplate 31 are mounted with exhaust mechanisms for discharging foreignsubstances and hot exhaust to prevent foreign substances from adheringto the wafer surface or to prevent an outflow of heat to the outside.

When a preset time elapses from the start of heating, the robot 8 takesout the wafer 7 and puts it on the cool plate 31. The cool plate 31 iscooled to a predetermined temperature by a cool plate control device 32and begins cooling when the wafer 7 is placed on it. When a preset timeelapses from the start of cooling, the robot 8 takes out the wafer 7 andreturns it to the wafer cassette 6.

FIG. 3 is a flow chart showing a sequence of processing from a step ofperforming a measurement/inspection using an electron beam to a step ofloading a wafer 7 in a wafer cassette 6. After the gate valve 11 (V2)installed between the sample chamber 12 and the load-lock chamber 9 isopen (S0002), the wafer 7 that has completed the measurement orinspection by the electron beam (S0001) is transferred into theload-lock chamber (S0003).

Next, the gate valve 11 is closed (S0004) and the interior of theload-lock chamber is leaked to the atmosphere (S0005). The load-lockchamber 9 is provided with a leakage pipe not shown which has mountedtherein a leak valve and a leak device. The leak valve is opened to leakthe load lock chamber 9.

Next, the gate valve 10 (V1) installed between the load-lock chamber 9open to the atmosphere and the wafer cassette 6 is opened (S0006), andthe wafer 7 is taken out of the load-lock chamber 9 by the transportrobot 8 (S0007). In this example, after the ambience of the wafer 7 isopen to the atmosphere, the wafer 7 is heated by the heater 30 (S0008).This is done for the following reason.

A sliding portion of the sample stage 13 (a portion through which twomembers contact each other as they move relative to each other) isapplied with a lubricant. As one example of lubricant, there isfluorinated lubricant. Fluorinated lubricant, particularly one combinedwith carbon, is chemically stable and inert and therefore can suitablybe used as a lubricant for the stage of scanning electron microscope.

Such a fluorinated lubricant, while it has an excellent characteristicfor enhancing the lubricating performance, is found to have a problemthat its low-molecular weight component adheres to the wafer. Alubricant (oil) that is refined to enhance the lubricating performancehas a predetermined molecular weight distribution. When a part of thelow-molecular weight component separates from the oil surface, it mayfly in many random directions and strike and bounce off the inner wallof the sample chamber because the chamber is vacuum. Further, it is alsoconceivable that the low-molecular weight component adhering to theinner wall of the sample chamber may come off and fly again.

A part of the low-molecular weight component flying in the samplechamber is discharged by the evacuation of the chamber. However, theinventors of this invention has found that a part of the flyinglow-molecular weight component repeats adhesion and separation beforeeventually sticking to the wafer.

A further investigation by the inventors shows that the low-molecularweight component adhering to the wafer may produce air bubbles in aresist during a subsequent resist application process. Because of theair bubbles the resist is formed thin, giving rise to a possibility ofpits being formed in a base material during a subsequent dry etchingprocess.

To reduce time and cost of the semiconductor process a semiconductorwafer cleaning process has come to be eliminated in recent years. Thus,a possibility arises that the low-molecular weight component may moveinto the resist application process while adhering to the semiconductorwafer. This further increases a possibility of failure.

As described above, in a vacuum chamber in which the sliding member isinstalled and the low-molecular weight components can fly, thelow-molecular weight components may adhere to the wafer 7 again. Forthis reason, this embodiment heats the semiconductor wafer to remove thelow-molecular weight components only after the wafer has beentransferred to a space of atmospheric pressure.

It is possible to start heating the wafer with the load-lock chamberevacuated and then to open the load-lock chamber to the atmosphere withthe wafer kept at a predetermined temperature. Under a circumstancewhere the low-molecular weight components occur only in the samplechamber but not in the load-lock chamber (for example, a moving memberapplied with a lubricant is not present in the load-lock chamber), aheating process may be executed before the load-lock chamber is open tothe atmosphere.

In this example, the wafer heating temperature is set to 200° C. and theheating time to 60 seconds. A result of test conducted by the inventorshas found that the low-molecular weight components adhering to the wafersurface mostly remain attached to the surface at the heating temperatureof less than 100° C., that at the heating temperature more than 100° C.they begin to be eliminated gradually, and that at 200° C. almost alllow-molecular weight components can be removed. (At the heatingtemperature of more than 200° C., although the heating time is slightlyreduced, the cooling time may become longer making the overall bakingtime longer.)

The heating temperature and time of the hot plate 30 are controlled bythe heater control device 33, and the wafer 7 can be heated to the aboveheating temperature for the duration described above. The controller 1is provided with an input device, not shown, for an operator to set adesired heating time and heating temperature.

Next, the wafer 7 removed of the low-molecular weight component byheating is cooled by the cooling mechanism 31 (S0009). The coolingmechanism 31 is controlled by the cooling mechanism control device 32 tocool the wafer 7 to a desired temperature for a desired time.

The cooling system employed in this embodiment is a water cooling typewhich cools the wafer by circulating pure water cooled to a presettemperature.

Considering the heat resistance of the wafer cassette and the effect ofheat on other wafers in the cassette, the wafer is preferably cooled toless than 50° C. (as close to room temperature as possible).

Although the wafer may be naturally cooled, since this will cause adelay in the semiconductor fabrication process, it is desired that acooling means be used to positively cool the wafer. Further, thetransport robot 8 is often installed in a space called a minienvironmentin which a highly clean environment is maintained. The minienvironmentis an enclosure which keeps its inner pressure high to prevent dust andparticles from entering from outside. It has a fan to introduce air fromoutside through a filter to increase the inner pressure. This air flowmay be used for cooling. It is also possible to provide a mechanism forintroducing cool air instead of a fan that generates a down flow in theminienvironment.

After being heated and cooled as described above, the wafer 7 isreturned to its original loaded position in the wafer cassette 6(S0010).

With the above processing complete, the wafer removed of thelow-molecular weight component can now be transferred to the nextsemiconductor fabrication process.

It is also conceivable to remove the low-molecular weight componentusing other devices after the measurement/inspection by the electronmicroscope is made. However, considering an additional step of takingout the wafer, that was returned to the wafer cassette, only for theremoval of low-molecular weight component, or a step of moving the wafercassette to other low-molecular weight component removing device, it isdesired in terms of efficiency that the low-molecular weight componentremoval processing be executed before the wafer is loaded into the wafercassette.

An example case has been described in which the wafer heating mechanismis installed on a wafer moving path between the load-lock chamber andthe wafer cassette. It is possible to provide a sidetrack for waferwhere the heater and the cooling mechanism may be installed.

Embodiment 2

FIG. 4 is a plan view of a scanning electron microscope in which ameasuring device 36 for measuring a contaminant in the sample chamber 12is mounted on the sample chamber having a microscope cylinder 35installed therein.

The measuring device 36 is controlled by the controller 1. A result ofmeasurement is sent to the controller 1 which, based on the result ofmeasurement, controls a heating unit 37. The heating unit 37 is mountedwith a heat exhaust unit 38 to release inner heat, a nitrogen leakdevice 39 to release the vacuum in the heating unit 37, and a leak valve40 that is opened to vent nitrogen into the heating unit 37.

The load-lock chamber 9 is mounted with an evacuation device 41 toevacuate the load-lock chamber 9 and an exhaust valve 42, and with aleak device 43 to release the vacuum in the load-lock chamber 9 and aleak valve 44.

The measuring device 36 is, for example, a quadrupole mass spectrometerwhich can identify a substance present in the sample chamber 12. Resultsof measurement made by the quadrupole mass spectrometer will beexplained by referring to FIG. 5 and FIG. 6. FIG. 5 represents a case inwhich the quadrupole mass spectrometer did not detect any low-molecularweight component, and FIG. 6 represents a case in which a low-molecularweight components was detected.

While in FIG. 5 no substances with mass number of more than 51 weredetected, FIG. 6 shows that substances with mass number of 69, 119 and169 were detected. These substances correspond in chemical expression toCF₃, C₂F₅ and C₃F₇ respectively, indicating that fluorinated substancesare volatilized in the vacuum.

If a result of measurement such as shown in FIG. 5 is obtained, it canbe decided that no contaminant is attached to the semiconductor wafersurface. So, the wafer is transported by the transport robot 8 from theload-lock chamber 9 to the wafer cassette 6 without passing it throughthe heating unit 37.

When on the other hand a result of measurement such as shown in FIG. 6is obtained, it is considered that contaminants including fluorinatedlubricant, e.g., perfluoropolyether (PFPE), and compounds of fluorineand carbon, constituents of PFPE, are adhering to the wafer surface. So,the wafer is transported to the heating unit 37 where it is heated andremoved of contaminants, before being carried by the transport robot 8to the wafer cassette 6.

As described above, according to the atmosphere in the sample chamber12, a decision is made as to whether contaminants are adhering to thewafer. Depending on this decision, whether the heating process isrequired or not is determined, eliminating the execution of unnecessaryheating process and allowing for both the removal of contaminants fromthe wafer and an improved efficiency of electron microscope measurement.

Although the above example makes a decision as to whether the heatingprocess needs to be executed, it is also possible to control the heatingtime and temperature according to the measurement result. Further, theheat resistance of a sample to be measured or inspected by the electronmicroscope may be taken into consideration in controlling the heatingtime and temperature. If the contaminant is detected to exceed apredetermined amount, the contaminant may be difficult to remove by theheating process. So, an error signal may be produced by the controller1.

Further, it is also possible to perform a control that involvesselectively heating the wafer when the amount of contaminant detected isin excess of a predetermined value and not performing the heating whenthe amount of contaminant is less than the predetermined value.

Embodiment 3

In the preceding embodiments, the contaminants are removed from asemiconductor wafer, a sample being transported, by heating the waferitself. In the following an example method will be explained which heatsa wall surface of a vacuum chamber such as sample chamber to preventcontaminants coming off the wall of the vacuum chamber from adhering tothe sample.

FIG. 7 shows an example construction of an electron microscopeincorporating a heating/cooling mechanism 51 capable of heating theinner wall of the sample chamber 12 to remove contaminants adhering tothe inner wall. This heating/cooling mechanism 51 heats the inner wallof the sample chamber 12 and then cools it to remove substances producedfrom the sliding member used in the sample stage 13.

It is noted, however, that since it directly heats the inner wall of thesample chamber, components of the lubricant that are evaporated duringheating may contaminate the inner wall of the sample chamber. To preventthis, it is desirable to install a mechanism that cools the sample stagewhile the sample chamber 12 is heated. This construction can selectivelyheat the inner wall of the sample chamber to remove contaminants withoutgiving the lubricant an adverse effect of heating.

Although the heating/cooling mechanism 51 in this example is constructedas a combination of a member for flowing a heat medium and a Peltierdevice cooling mechanism, other forms of heating/cooling mechanism maybe used. For example, a combination of lamp heating or resistive heatingand a Peltier device cooling mechanism, or other combinations may beused.

In an electronic microscope in which the wafer 7 is carried on thesample holder (not shown) as it is transferred between the load-lockchamber 9 and the sample chamber 12, the sample holder, when it issituated in the sample chamber, can be heated along with the samplechamber 12 to prevent contaminants from diffusing out of the samplechamber.

FIG. 8 illustrates an example construction of an electronic microscopeincorporating a voltage control electrode 45 to control a voltage in aspace in which a sample is placed. There is a retarding technique whichsuppresses aberration by radiating an electron beam of low accelerationenergy against a semiconductor wafer which is fragile to an electronbeam of high acceleration energy. The retarding technique is a methodwhich enhances the acceleration energy of the electron beam as it passesthrough an object lens by applying a negative voltage to the sample andat the same time lowering the acceleration energy of the electron beamas it reaches the sample. An electrode that can properly apply such aretarding voltage to the sample even when the sample is covered with aninsulating film, is the voltage control electrode 45. Details of thevoltage control electrode 45 are described in, for example,JP-A-9-171791.

The voltage control electrode 45 is arranged in a directionperpendicular to an optical axis of the electron beam to cover a rangein which the sample is moved by the sample stage. If contaminants adhereto this voltage control electrode 45, since it faces the sample, thecontaminants may diffuse over a wide range of sample surface by thedispersion of the contaminants and their separation from the electrode.

To solve this problem, a heating/cooling mechanism 52 to heat and coolthe voltage control electrode 45 is installed in the sample chamber. Inthis example, since a voltage control electrode, one of the portionsthat can exert an evil influence on the microscope performance whenadhered to by contaminants, can be selectively heated, measurement orinspection can be made without contaminating the sample.

FIG. 9 shows an example construction of a microscope incorporating aheating/cooling mechanism 53 to directly heat the stage 13. In thesample chamber 12 it is possible that contaminants are moving around.Therefore, after measurement or inspection by the electronic microscopeis completed, the sample or the sample holder carrying it is heated asthe sample is moved out of the sample chamber 12 before the gate valve11 is opened. This makes it possible to clean the sample withoutdiffusing contaminants out of the sample chamber.

Embodiment 4

Example methods and constructions for removing contaminants followingmeasurement and inspection have been described. An example apparatuscapable of suppressing adhesion of contaminants to the inner wall of theload-lock chamber will be explained as follows.

The load-lock chamber 9 is a space to preliminarily exhaust the sampleambience when introducing the sample into the sample chamber 12. Amongapparatus that continuously perform measurement and inspection onwafers, there is one that has a plurality of load-lock chambers so thatas soon as the measurement of one wafer is finished, the next wafer isintroduced into the sample chamber.

FIG. 10 is a plan view of a charged particle beam apparatus and aload-lock chamber. Here, a charged particle beam apparatus capable ofhaving two wafer cassettes 6 is taken as an example. In this example,wafers are carried by robot arms 8 a, 8 b from the wafer cassettes 6 a,6 b into load-lock chambers 9 a, 9 b. The wafers transferred into theload-lock chambers 9 a, 9 b are then introduced alternately into thesample chamber 12 where they are subjected to measurement and inspectionusing an electron beam. Having undergone the measurement and inspection,the wafers are moved back into the wafer cassette 6 through the samepath as when they were transferred into the sample chamber 12.

In this process, to enhance throughput, the wafer must be kept standingby in the load-lock chamber maintained at vacuum so that as soon as thepreceding measurement is finished, the wafer can be introduced.

However, keeping the wafer standing by for a long period of time in thevacuum chamber may cause a problem of wafer contamination in the vacuumchamber as explained earlier.

In light of this problem, the construction of this example has the waferstand by in the load-lock chamber maintained at the atmospheric pressureexcept for the evacuation time.

FIG. 11 shows a sequence of operation when a wafer is kept standing bywith the load-lock chamber maintained at the atmospheric pressure.“Load-lock a” explains an evacuation time of the load-lock chamber 9 a(denoted v), the wafer transfer to and from the sample chamber 12, andopen-close operation times (shown shaded) of gate valves 11 a, 11 b (notshown) provided in the load-lock chamber 9 a. A wafer is carried betweenthe sample chamber 12 and the load-lock chamber 9 by a moving mechanismnot shown.

“Robot arm a” explains a time taken by the robot arm 8 a to transfer thewafer between the wafer cassette 6 a and the load-lock chamber 9 a(transfer from load-lock chamber 9 a to wafer cassette 6 a isrepresented by a horizontal line and transfer from wafer cassette 6 a toload-lock chamber 9 a is represented by a vertical line).

“Load-lock b” and “robot arm b” similarly represent times spent in thewafer cassette 6 b, load-lock chamber 9 b, gate valves 10 b, 11 b andsample chamber 12.

As explained earlier, a risk of wafer contamination is higher in avacuum state than in the atmospheric pressure. It is therefore desirableto make the time that the wafer is placed in the vacuum chamber as smallas possible. Considering these conditions, the wafer in this example ismade to stand by in the load-lock chamber at the atmospheric pressureexcept for the evacuation time.

More specifically, as explained in FIG. 11, during the time whichelapses after the wafer has been introduced into the load-lock chamber 9a by the robot arm 8 a until it is introduced into the sample chamber12, a standby time for the wafer to stand by at the atmospheric pressureis provided, excluding the evacuation time “v” to a specified vacuumlevel and the wafer transfer time.

To execute this processing, the time required by the action associatedwith the wafer transfer and the time it takes for the load-lock chamberto reach a predetermined level of vacuum are subtracted from a plannedmeasurement end time of another load-lock chamber to calculate aremaining time. This remaining time is made a “standby time”. After thewafer has been introduced to the load-lock chamber, the standby time canbe determined by subtracting the time it takes for the load-lock chamberto reach a predetermined vacuum level from the planned end time of theprevious measurement.

With the above construction, it is possible to eliminate thecontamination risk caused by putting the sample in a vacuum state andalso improve throughput by introducing the wafer into the sample chamberimmediately after the end of the preceding measurement.

From the standpoint of simplifying the sequence, it is preferred to havethe wafer stand by in a vacuum state and introduce the next wafer afterthe end of the preceding measurement is detected. However, this examplefocuses on the problem of wafer contamination and provides a standbytime for reducing the evacuation time, thereby suppressing the wafercontamination without degrading the throughput.

It should be further understood by those skilled in the art thatalthough the foregoing description has been made on embodiments of theinvention, the invention is not limited thereto and various changes andmodifications may be made without departing from the spirit of theinvention and the scope of the appended claims.

1. A charged particle beam apparatus comprising: a charged particlesource; a sample stage which puts a sample to be radiated with a chargedparticle beam emitted from the charged particle source; a vacuum chamberto evacuate a space surrounding the sample to a vacuum; a preliminaryexhaust chamber to preliminarily evacuate a space including a sampletaken out from a sample cassette to be introduced into the vacuumchamber; and a heating device disposed between the preliminary exhaustchamber and the sample cassette, the heating device being configured toheat the sample before the sample is introduced into the sample cassetteand when or after the preliminary exhaust chamber is opened to theatmosphere after the sample has been radiated with the charged particlebeam, wherein the preliminary exhaust chamber is disposed between thevacuum chamber and the heating device.
 2. A charged particle beamapparatus according to claim 1, wherein the heating device heats thesample to a temperature higher than 100° C. and lower than 200° C.
 3. Acharged particle beam apparatus according to claim 2, wherein theheating device heats the sample during a time in which fluorocarboncompounds adhering to the sample can be removed.
 4. A charged particlebeam apparatus according to claim 1, wherein a measuring device isinstalled in the vacuum chamber to measure contaminants in the vacuumchamber and, when the contaminants are detected or more than apredetermined amount of the contaminants is detected by the measuringdevice, the sample is heated.